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<p>rand()和random()实际并不是一个真正的伪随机数发生器，在使用之前需要先初始化随机种子，否则每次生成的随机数一样。</p>
<p>arc4random() 是一个真正的伪随机算法，不需要生成随机种子，因为第一次调用的时候就会自动生成。而且范围是rand()的两倍。在iPhone中，RAND_MAX是0x7fffffff (2147483647)，而arc4random()返回的最大值则是 0x100000000 (4294967296)。</p>
<p>精确度比较：arc4random()  &gt;  random()  &gt;  rand()。</p>
<ul>
<li>获取一个随机整数范围在：[0,100)包括0，不包括100</li>
</ul>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">// 方法1</span><br><span class="line">int x = arc4random() % 100;</span><br><span class="line">// 方法2</span><br><span class="line">int x = arc4random_uniform(100);</span><br></pre></td></tr></table></figure>

<ul>
<li>获取一个随机数范围在：[500,1000]，包括500，包括1000</li>
</ul>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">// 方法1</span><br><span class="line">int y = (arc4random() % 501) + 500;</span><br><span class="line">// 方法2</span><br><span class="line">int y = arc4random_uniform(500 + 1) + 500;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<ul>
<li>获取一个随机整数，范围在[from,to]，包括from，包括to</li>
</ul>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">// 范围在[from,to]</span><br><span class="line">- (int)getRandomNumber:(int)from to:(int)to</span><br><span class="line">&#123;</span><br><span class="line">    return arc4random_uniform(to - from + 1) + from;</span><br><span class="line">//    return (arc4random() % (to - from + 1)) + from;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>来源：<a target="_blank" rel="noopener" href="https://xiaohu860.gitbooks.io/ios/content/xijie_1.html">https://xiaohu860.gitbooks.io/ios/content/xijie_1.html</a></p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line">生成<span class="number">0</span>-x之间的随机正整数</span><br><span class="line"><span class="type">int</span> value =arc4random_uniform(x ＋ <span class="number">1</span>);</span><br><span class="line"></span><br><span class="line">生成随机正整数</span><br><span class="line"><span class="type">int</span> value = arc4random();</span><br><span class="line"></span><br><span class="line">通过arc4random() 获取<span class="number">0</span>到x<span class="number">-1</span>之间的整数的代码如下：</span><br><span class="line"><span class="type">int</span> value = arc4random() % x; </span><br><span class="line"> </span><br><span class="line">获取<span class="number">1</span>到x之间的整数的代码如下: </span><br><span class="line"><span class="type">int</span> value = (arc4random() % x) + <span class="number">1</span>; </span><br><span class="line"> </span><br><span class="line">最后如果想生成一个浮点数，可以在项目中定义如下宏：</span><br><span class="line"><span class="meta">#<span class="keyword">define</span> ARC4RANDOM_MAX      0x100000000 </span></span><br><span class="line"> </span><br><span class="line">然后就可以使用arc4random() 来获取<span class="number">0</span>到<span class="number">100</span>之间浮点数了（精度是rand()的两倍），代码如下：</span><br><span class="line"><span class="type">double</span> val = floorf(((<span class="type">double</span>)arc4random() / ARC4RANDOM_MAX) * <span class="number">100.0</span>f);</span><br></pre></td></tr></table></figure>



<p>随机色</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">#define RGBColor(r, g, b) [UIColor colorWithRed:(r)/255.0 green:(g)/255.0 blue:(b)/255.0 alpha:1]</span><br><span class="line"></span><br><span class="line">#define RGBAColor(r, g, b ,a) [UIColor colorWithRed:(r)/255.0 green:(g)/255.0 blue:(b)/255.0 alpha:a]</span><br><span class="line"></span><br><span class="line">//随机色</span><br><span class="line">#define RandColor RGBColor(arc4random_uniform(255), arc4random_uniform(255), arc4random_uniform(255))</span><br></pre></td></tr></table></figure>



<p>参考：<a target="_blank" rel="noopener" href="http://nshipster.cn/random/">http://nshipster.cn/random/</a></p>
<p><a target="_blank" rel="noopener" href="http://iphonedevelopment.blogspot.com/2008/10/random-thoughts-rand-vs-arc4random.html">http://iphonedevelopment.blogspot.com/2008/10/random-thoughts-rand-vs-arc4random.html</a></p>
</div></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="mailto:undefined">kyren</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="http://huluo666.gitee.io/2016/04/21/iOS 随机数/">http://huluo666.gitee.io/2016/04/21/iOS 随机数/</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span class="post-copyright-info">本博客所有文章除特别声明外，均采用 <a target="_blank" rel="noopener" href="https://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA 4.0</a> 许可协议。转载请注明来自 <a href="http://huluo666.gitee.io">Kyren's Blog</a>！</span></div></div><div class="post-meta__tag-list"><a class="post-meta__tags" href="/tags/iOS/">iOS</a></div><nav id="pagination"><div class="prev-post pull-left"><a href="/2016/04/21/iOS%20UITableView%E4%B8%8EUIScrollView%E5%B5%8C%E5%A5%97%E6%8B%96%E5%8A%A8%E6%89%8B%E5%8A%BF%E5%86%B2%E7%AA%81%E9%97%AE%E9%A2%98/"><i class="fa fa-chevron-left">  </i><span>iOS UITableView与UIScrollView嵌套拖动手势冲突问题</span></a></div><div class="next-post pull-right"><a href="/2016/04/20/iOS%20%E5%AD%97%E9%9D%A2%E9%87%8F%E8%AF%AD%E6%B3%95/"><span>iOS 字面量语法</span><i class="fa fa-chevron-right"></i></a></div></nav></div></div><footer><div class="layout" id="footer"><div class="copyright">&copy;2022 By kyren</div><div class="framework-info"><span>驱动 - </span><a target="_blank" rel="noopener" href="http://hexo.io"><span>Hexo</span></a><span class="footer-separator">|</span><span>主题 - </span><a target="_blank" rel="noopener" href="https://github.com/Molunerfinn/hexo-theme-melody"><span>Melody</span></a></div><div class="footer_custom_text">hitokoto</div><div class="busuanzi"><script async src="//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script><span id="busuanzi_container_page_pv"><i class="fa fa-file"></i><span id="busuanzi_value_page_pv"></span><span></span></span></div></div></footer><i class="fa fa-arrow-up" id="go-up" aria-hidden="true"></i><script src="https://cdn.jsdelivr.net/npm/animejs@latest/lib/anime.min.js"></script><script src="https://cdn.jsdelivr.net/npm/jquery@latest/dist/jquery.min.js"></script><script src="https://cdn.jsdelivr.net/npm/@fancyapps/fancybox@latest/dist/jquery.fancybox.min.js"></script><script src="https://cdn.jsdelivr.net/npm/velocity-animate@latest/velocity.min.js"></script><script src="https://cdn.jsdelivr.net/npm/velocity-ui-pack@latest/velocity.ui.min.js"></script><script src="/js/utils.js?version=1.9.0"></script><script src="/js/fancybox.js?version=1.9.0"></script><script src="/js/sidebar.js?version=1.9.0"></script><script src="/js/copy.js?version=1.9.0"></script><script src="/js/fireworks.js?version=1.9.0"></script><script src="/js/transition.js?version=1.9.0"></script><script src="/js/scroll.js?version=1.9.0"></script><script src="/js/head.js?version=1.9.0"></script><script src="/js/search/local-search.js"></script><script>if(/Android|webOS|iPhone|iPod|iPad|BlackBerry/i.test(navigator.userAgent)) {
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